Cathode plate for zinc recovery



1956 J, F. VANDERPOOL 2,736,697

CATHODE PLATE FOR ZINC RECOVERY Filed May 1, 1951 2 Sheets-Sheet 1 /6 mm? laz- INVENTOR. Jblm F l/anderpool BY 4 WM 54 I fiv- Feb. 28, 1956 J. F. VANDERPOOL 2,736,697

CATHODE PLATE FOR ZINC RECOVERY Filed May 1, 1951 2 Sheets-Sheet 2 INVENTOR.

Jblm E Vanderpool i a fi l United States Patent CATHODE PLATE FOR ZINC RECOVERY John Franklin Vanderpool, Smelterville, Idaho Application May 1, 1951, Serial No. 223,941

3 Claims. (Cl. 204-281) My present invention relates to improvements in a cathode plate for zinc recovery.

The present practice in electrolytic zinc refineries is to deposit by electrolytic action a sheet of zinc, upon a cathode plat'e. This plateis sometimes referred to as a stripping cathode, since the deposited sheet of metal is stripped from the plate and the plate is used again for further deposits. It is the usual practice to separate the deposited sheet of zinc by means of a wide chisel in the hand of an operator who drives the chisel edge between the edge of the deposited sheet of metal and the surface-of the cathode plate. The cathode plate is constructed of aluminum that is rolled to give it the desired hardness. The plate has one edge welded to a support bar by which it is suspended in the electrolytic solution. The supporting bar serves also to provide electrical contact for the plate.

It has been proposed to cast these cathode plates, but such a procedure does not work satisfactorily as the cast plates are quickly attacked by the electrolytic solution and the deposited sheet cannot be stripped therefrom. A rolled hardened sheet of pure aluminum is at present used because it withstands the attack of the solution where it is immerged in the solution, and the deposited sheet of zinc can be readily stripped. The aluminum plate, however, is severely attacked just above the level of the electrolytic solution. This results in plates becoming so thin at the solution line that they have to be discarded. It has been proposed that in order to continue the use of the plate that the two sections be welded together after they have been eaten apart above the acid line. However, this is not satisfactory for the reason that the welded joint does not withstand the action of the solution and is quickly destroyed.

It is the purpose of my invention to provide a novel cathode plate that is thickened and hardened a short distance from its attaching edge so that the thickened and hardened portion will lie in a zone just above the level of the electrolytic solution and prolong the useful life of the plate by its increased resistance to attack by the electrolytic solution.

It is a further purpose of my invention to provide a novel method of treating a cathode plate to increase its thickness and its resistance to attack by the electrolytic solution along a line slightly above the level of the solution in which the plate is placed.

The nature and advantages of my invention will appear more fully from the following description and the accompanying drawings illustrating a preferred form thereof. It should be understood however, that the drawings and description are illustrative only and are not intended to limit the invention except insofar as it is limited by the claims.

In the drawings:

Figure 1 is a somewhat diagrammatic view illustrating a cross section of an electrolytic recovery tank in which my improved cathode plate is used;

2,736,697 Patented Feb. 28, 1956 Figure 2 is an enlarged cross section taken vertically through a cathode plate and its support bar and illustrating how the zinc is deposited in a sheet on the plate;

Figure 3 is a fragmentary perspective view illustrating the manner in which the deposited zinc sheet is stripped from the cathode plate;

Figure 4 is a somewhat diagrammatic view illustrating the fashion in which a cathode plate is upset to produce an increased thickness at the zone just above the level of the electrolytic solution;

Figure 5 is a perspective view illustrating the initial step in treating the plate according to my method;

Figure 6 illustrates a second step in the method;

Figure 7 illustrates a third step in the method; and

Figure 8 is an enlarged fragmentary view illustrating how the sheet is worked to produce the thickened hardened zone.

The cathode plates generally in use in this area for the electrolytic recovery of zinc are made of a pure aluminum which is rolled in sheets and hardened somewhat by the rolling. By pure aluminum, I mean commercially pure aluminum plate. The particular size of the plate may of course vary, but ordinarily the ones used with which I am familiar are about .160 inch thick. As illustrated in Figure l, the cathode plate 10 is welded to a header bar 11 to which electrical contact is made by a support clamp 12. The bar 11 supports the plate 10 in a tank 13 which contains the electrolytic solution. The tank usually has supporting members 14 of suitable non-conducting material such as wood for supporting the header bar 11. The level of the electrolytic solution in the tank 13 is indicated at 15. The distance from the header bar 11 to the level of the solution at 15 is in the neighborhood of 3 inches. In the use of the plates it is found that the principal area of attack of the solution on the plate occurs in a zone extending upwardly from the level of the solution about /5 inch to inch. It has long been considered desirable to protect this particular area of the plate and various proposals have been advanced for this purpose such as the coating of the plate, the application of a sleeve thereto etc. None of these methods have come into use in the area in which I am acquainted.

According to my invention I provide the plate 10 with a thickened hardened zone 16 that extends from a slight distance below the level of the electrolytic solution far enough upward to be well above the Zone of greatest attack which is in the first half inch above the solution level. This thickened zone 16 blends into the surface of the plate that is in the solution with a smooth curve as indicated at 17 so as not to interfere with the stripping of the deposited zinc from the sheet. The deposited zinc sheet is illustrated in Figures 2 and 3 at 18. It is customary for the operator to strip the zinc sheet 18 from the plate 10 by starting it with a chisel 19. The operator first strikes the cathode plate a sharp blow above the top level of the zinc deposit 18 to break loose the edge of the deposit from the plate 10. Once the stripping is started it is an easy matter to remove the entire sheet of zinc deposited on the plate.

The thickened hardened zone 16 of the plate is formed by upsetting the metal and working it as described hereinafter. By so forming the cathode plate 10, I have been able to greatly improve the life thereof. For example, in a comparative test while an untreated plate 10 was losing .052 inch thickness just above the level of the solution, my improved treated plate under the same conditions in the same solution, lost .035 inch thickness. The increased resistance of the thickened portion 16, as evidenced by the above figures, is only one factor in the life increase of my improved plate. The other factor is the increased thickness at the zone of greatest attack..

I prefer to increase the thickness to approximately twice that of the original plate at the point of maximum thickness of the portion 16. Thus if the plate would be destroyed at the same rate, the additional life would be double that of the original plate. The rate of destruction is reduced in my treated plate by more than onefourth when compared with the rate of destruction of the untreated plate.

Referring now to Figures 4-8 inclusive, these figures illustrate the manner in which a cathode plate it is treated to produce the enlarged and hardened section 16. The plate is initially bent in a smooth curve at 20 as illustrated in Figures 4 and 5. This bend extends parallel to the attaching edge 1th: of the plate. The plate is then secured in such a fashion that it will not curl up on opposite sides of the bend 2t) and the sheet is forced back to fiat position gradually, beginning at one end of the plate and working toward the other end.

As an example of how the sheet may be held and worked, Figure 4 illustrates an anvil 21 on which the sheet is placed and two clamps 22 and 23 are used to hold the sheet from curling up. The anvil has guide ribs 24 and 25 between which the sheet is located. The clamps are adjusted by screws 26 and 27. it is obvious of course that any suitable means can be used for holding the plate 10 and the means shown here is merely an example. With the sheet 10 in place as illustrated, pres sure is applied to the bend 21 as illustrated by the plungers 28. These plungers may be hammers or they may be just pressed down by a steady force. The important feature is that they must work progressively lengthwise of the bent portion 20 of the plate to push the metal down against the anvil 21. For example, in Figure 5, the pressure would be applied first at 30 at the left hand end of the sheet 10 and the sheet would be flattened at this point until the bottom surface contacted the anvil. Then the plunger 28 would move to the right along the sheet 10 and flatten another portion. In this way the tension in the bent portion of the metal is utilized to upset and thicken the portion that is being flattened. In Figure 5 the upsetting has been carried out to the point 31. This point is also indicated in Figure 8 at 31, and partial flattening has occurred for a substantial distance to the left of the point 31 in Figure 8.

After the first thickening operation it may be necessary, in order to get the desired thickness and hardness, to again bend and flatten the sheet. The second bend is illustrated at 29a in Figure 6 where it will be noted that the thickness at the apex of the bend has been increased from the thickness shown in Figure 5, The bend 20 may be formed in either direction and repeated bending and flattening can be carried out until the desired thickness is obtained. In Figure 7 the bend 20b is in the opposite direction to that in Figures 5 and 6 and the material at the apex of the bend has been increased in thickness over that in Figure 6.

My improved method can be carried out mechanically or by hand. I have made plates with thickened zones 16 entirely by hand and increased the thickness in zone 16 to twice that of the body of the plate with no more than four bends. The bending and flattening of the metal work hardens it and I attribute part of its resistance to attack by the solution to this fact. The method of forming the thickened portion provides the smooth curved blending of the thickened portion with the plain portion of the sheet which is highly essential to preserve the ease of stripping the zinc from the plate.

It is believed that the nature and advantages of my invention will be apparent from the foregoing description. Having thus described my invention, I claim:

1. A stripping cathode plate for electro deposition of metal comprising a rolled metal sheet having an edge portion adapted for attachment to a suspension means for suspending the sheet in an electrolyte and having a rectangular, fiat body portion of uniform thickness spaced from said edge portion to receive the deposited metal, said sheet having a portion connecting the edge portion and body portion of substantially greater thickness than the other portions and adapted to be partly in and partly out of the electrolyte, said portions all being composed of the same metal, the metal in said thickened portion being upset, and the opposite surfaces of said thickened portion being curved to merge smoothly with the body portion.

2. A stripping cathode plate for receiving a deposit of metal from an electrolytic bath, comprising a rectangular sheet of rolled metal having one side edge adapted for attachment to a header bar for supporting the plate in the bath and conducting current from the plate, said plate having an integral thickened rib portion which is harder than the rest of the plate and which extends from end to end of the plate adjacent to, but spaced from, the header bar receiving side edge, said plate being fiat and of substantially uniform thickness throughout except for said rib portion, the thickened rib portion being entirely of the same metal as the remainder of the sheet and having its surface merging with the remainder of the sheet surface and forming an uninterrupted continuation thereof.

3. A stripping cathode plate for receiving a deposit of zinc from an electrolytic bath comprising a flat sheet of aluminum having a straight side edge for attachment to a header bar for supporting the plate in the bath and conducting current from the plate, said plate having an integral thickened rib portion of aluminum which is harder than the rest of the plate and which extends from end to end of the plate adjacent to, but spaced from the header bar receiving side edge, said plate being of substantially uniform thickness except for said rib portion, said rib portion tapering gradually from a maximum thickness of about twice the thickness of the rest of the plate along the center of the rib portion to the thickness of the rest of the plate at its side edges.

References Cited in the file of this patent UNITED STATES PATENTS 1,347,189 Stevens a- July 20, 1920 1,433,618 Hogaboom Oct. 31, 1922 1,674,318 Carr -.June 19, 1928 1,836,368 Eppensteiner Dec. 15, 1931 2,023,638 Lawson Dec. 10, 1935 2,048,854 Dyer July 28, 1936 2,324,342 Wellman July 13, 1943 2,536,877 Emanuel Jan. 2, 1951 

1. A STRIPPING CATHODE PLATE FOR ELECTRO DEPOSITION OF METAL COMPRISING A ROLLED METAL SHEET HAVING AN EDGE PORTION ADAPTED FOR ATTACHMENT TO A SUSPENSION MEANS FOR SUSPENDING THE SHEET IN AN ELECTROLYTE AND HAVING A RECTANGULAR, FLAT BODY PORTION OF UNIFORM THICKNESS SPACED FROM SAID EDGE PORTION TO RECEIVE THE DEPOSITED METAL, SAID SHEET HAVING A PORTION CONNECTING THE EDGE PORTION AND BODY PORTION OF SUBSTANTIALLY GREATER THICKNESS THAN THE OTHER PORTIONS AND ADAPTED TO BE PARTLY IN AND PARTLY OUT OF THE ELECTROLYTE, SAID PORTIONS ALL BEING COMPOSED OF THE SAME METAL, THE METAL IN SAID THICKENED PORTION BEING UPSET, AND THE OPPOSITE SURFACES OF SAID THICKENED PORTION BEING CURVED TO MERGE SMOOTHLY WITH THE BODY PORTION. 